Injection moulding tool

ABSTRACT

An injection moulding tool for producing at least one injection-moulded part with an outer shape and an inner shape includes at least one cavity and, for every cavity, one hot-runner nozzle connected thereto, which has an annular nozzle mouth for injecting at least one melt into the cavity. The at least one cavity is formed by a cooled die, which forms the outer form for the outer shape of the injection-moulded part to be produced, and by a core, which forms the inner form for the inner shape of the injection-moulded part to be produced. The hot-runner nozzle has a nozzle core and a hollow needle, which can be moved along the nozzle core for opening and closing the annular nozzle mouth. The nozzle core protrudes beyond the annular nozzle mouth of the hot-runner nozzle and the nozzle core forms the core of the cavity of the injection mould.

TECHNICAL FIELD

The invention relates to an injection moulding tool for producing atleast one injection-moulded part with an outer shape and an inner shape.The injection-moulded part comprises at least one cavity andrespectively one hot-runner nozzle connected to the cavity having anannular nozzle mouth for injecting at least one melt into the cavity.

TECHNICAL BACKGROUND

Plastic containers or container-like plastic parts are frequentlyproduced by means of injection moulding in injection moulding tools. Aninjection moulding tool for such parts comprises at least one cooledcavity in which the plastic in liquid form is injected via a hot-runnernozzle through a nozzle mouth. The cavity is formed by a die which formsthe outer form of the container to be produced and a core which formsthe inner form of the container to be produced. The holt melt solidifiesafter injection in the cooled cavity and can be ejected after openingthe injection moulding tool or the cavity.

In the known injection moulding tools for plastic containers with aclosed base, the injection point for injecting the plastic is arrangedcentrally in the base region and the melt flows from the central regioninto a peripheral region of the injection-moulded part. In the simplestdesign of the injection moulding tool, the hot-runner nozzle is arrangedon the die side, which also allows the manufacture of containers havinga small circumference, high or narrow containers or blanks for plasticbottles.

In some injection moulding tools, simple, small-dimensioned hot-runnernozzles can also be arranged on the core side. However, this assumesthat the container has a sufficiently large circumference so that thecore of the injection moulding tool which extends around the hot-runnernozzle can be cooled.

In the case of container-like injection-moulded parts such as, forexample tube heads or containers which have a central opening in thebase, a punctuate injection is not suitable. Such injection-mouldedparts are injected on the die side annularly around the opening, whereinhere also the melt flows from the central region into the peripheralregion of the injection-moulded part. Examples are shown in WO14044647,EP1504873, U.S. Pat. No. 9,050,747 and WO15059020.

DESCRIPTION OF THE INVENTION

It is the object of the invention to provide an injection moulding toolwhich allows a peripheral annular injection to produce injection-mouldedparts in which a central injection is unsuitable or not desired.

The injection moulding tool for producing at least one injection-mouldedpart with an outer shape and an inner shape comprises at least onecavity and respectively one hot-runner nozzle connected to the cavitywith annular nozzle mouth for injecting at least one melt into thecavity. The at least one cavity is formed by a cooled die which formsthe outer form for the outer shape of the injection-moulded part to beproduced and by a core which forms the inner form for the inner shape ofthe injection-moulded part to be produced. The hot-runner nozzle has anozzle core and a hollow needle which is displaceable along the nozzlecore for opening and closing the annular nozzle mouth. The nozzle coreprotrudes beyond the annular nozzle mouth of the hot-runner nozzle andforms the core of the cavity of the injection moulding tool.

In such an injection moulding tool, therefore the hot-runner nozzle atthe same time forms the inner form for the inner shape of theinjection-moulded part to be produced by means of the nozzle core whichis axially not movable in the hot-runner nozzle. That is, the region ofthe nozzle core protruding over the annular nozzle mouth forms with itslateral surface and its front side the inner form of theinjection-moulded part. In some places the front side of the nozzle corecan contact the die so that recesses are formed in the injection-mouldedpart. The melt is injected into an annular gap of the cavity by theannular nozzle mouth of the hot-runner nozzle, which surrounds thenozzle core, and flows at least partially along the nozzle core in thedirection of the longitudinal axis of the hot-runner nozzle. The meltthen cools in the cavity and solidifies to form the injection-mouldedpart. Upon opening the injection moulding tool, i.e. after the die andcore have been pulled apart, the injection-moulded part is ejected.

The injection moulding tool therefore allows the production of one-pieceinjection-moulded parts by annular injection from a peripheral region,wherein the melt flows from the peripheral region into a central regionin the direction of the longitudinal axis of the hot-runner nozzle.Thus, for example, plastic containers or container-like parts can beproduced in which a central injection in the base region—being thispunctuate or annular—is not possible or not desired. For example, when anon-plastic part, for example, an injection needle, is to beover-moulded in the central base region.

Container-like injection-moulded parts means, in addition to plasticcontainers also injection-moulded parts or plastic parts which have aninner shape and an outer shape.

That is base and wall can also have recesses or the injection-mouldedparts are closed or closable containers only provided with additionalelements.

In some embodiments the nozzle core can comprise an inner activelycooled cooling core, in particular a water-cooled cooling core and anouter core. The outer core forms the inner form of the cavity and can beformed according to the inner shape of the desired injection-mouldedpart. The cooling core can have a circular cylindrical structure andallows an efficient cooling of the outer core through the nozzle. It canbe used unchanged in its form for injection moulding tools havingdifferent cavities, by merely adapting the outer core to the desiredinner form. Cooling core and outer core can be configured in such amanner that the front side of the cooling core forms a part of the innerform and the outer core encloses the cooling core in a sleeve-likemanner. An actively cooled nozzle core can be used with a diameter from3 mm.

In some embodiments, upstream of the nozzle mouth the nozzle core cancomprise at least one insulating jacket along which the hollow needle isguided. The insulating jacket can be made of ceramic or a lowheat-conducting metal or a low heat-conducting metal alloy (e.g. achromium steel). A low heat-conducting metal/metal alloy should have alower thermal conductivity than the metal alloy for the heated parts ofthe hot-runner nozzle. Preferably a thermal conductivity of less than50λ (W/(m*K)) (measured according to DIN V 4108-4).

In some embodiments, the insulating jacket extends as far as the cavity.However, in order to achieve an even better cooling of the cavity, theouter core which is cooled can have a circumferential shoulder or acircumferential flange in the region of the nozzle mouth. Thecircumferential shoulder/the circumferential flange forms one side ofthe nozzle mouth and can form a part of the cavity so that the cavity iscompletely formed by the cooled die plate, the cooled core plate and thecooled nozzle core of the hot-runner nozzle. The insulating jacket inthis case reaches as far as the circumferential shoulder/flange.

In some embodiments, upstream of the nozzle mouth the outer core canhave a circumferential recess in order to reduce heat or cold bridgesbetween nozzle core and the heated parts of the hot-runner nozzle.Preferably the circumferential recess is arranged in the front region ofthe hot-runner nozzle in which the melt is guided closely along thenozzle core.

In some embodiments, the hot-runner nozzle can be a co-injection nozzlefor injection of a concentrically layered melt flow into the cavity. Inthis case, the layered melt flow can consist of two outer layers of afirst melt and an inner layer of a second melt. The inner layer can, forexample, be a so-called barrier layer. In particular in the case ofmultilayer containers or container-like injection-moulded parts, whichhave complex structures such as ribs, projections and recesses in thebase region, as a result of turbulence of the layered melt flow it canbe disadvantageous or impossible to inject this from a central point.

In some embodiments a cooled die plate can form the die.

In some embodiments the core can be cooled and arranged in a cooled coreplate.

In some embodiments the hot-runner nozzle can be mounted in the cooledcore plate by means of a sealing ring.

In some embodiments the hot-runner nozzle can be constructed like theco-injection nozzles described in the International Patent ApplicationsPCT/EP2015/071667 and PCT/EP2015/071668 of the same applicant with thedifference that the valve needle is a hollow needle and the co-injectionnozzle has the previously described nozzle core.

Such a hot-runner nozzle or co-injection nozzle for producing multilayerinjection-moulded parts comprises a first melt supply channel for afirst melt; a second melt supply channel for a second melt; a centralbore; a hollow needle received axially movably in the central bore foropening and closing an annular nozzle mouth; an annular inner meltchannel which is formed by the central bore and the hollow needle in theupstream-directed region of the co-injection nozzle and which isfluidically connected to the first melt supply channel; an annularcentral melt channel which is fluidically connected to the second meltsupply channel and which extends around the annular inner melt channel;an annular outer melt channel, which is connected fluidically to thefirst melt supply channel and which extends around the annular centralmelt channel; wherein the inner, central and outer melt channel arefluidically combined in the region of the nozzle tip to form aconcentrically layered melt flow. The previously described nozzle corewhich at the same time can form the core of a cavity is arranged in thehollow needle.

The co-injection nozzle further comprises a nozzle body and a meltdistributor insert which comprises the central bore. The meltdistributor insert is received in a central bore of the nozzle body andpreferably has a cylindrical shape which tapers towards the nozzle tip.At least one distributor channel for the first melt and at least onedistributor channel for the second melt are formed along the jacketsurface or the outer surface, which channels guide the respective meltsin the direction of the nozzle tip.

The at least one distributor channel for the first melt can be connectedfluidically upstream to the first melt supply channel and the annularinner melt channel and can be connected downstream to the annular outermelt channel. The at least one distributor channel for the first meltcan have branchings downstream in order to distribute the first meltmore uniformly to the annular outer melt channel.

The at least one distributor channel for the second melt can beconnected fluidically upstream to the second melt supply channel and canbe connected downstream to the annular central melt channel. The atleast one distributor channel for the second melt can have branchingsdownstream in order to distribute the second melt more uniformly to theannular central melt channel. This allows an efficient and uniformdistribution of the melts to annular melt channels having diameters ofmore than 40 mm.

The co-injection nozzle can further comprise a dividing sleeve whoseinner surface partially forms the annular central melt channel and whoseouter surface partially forms the annular outer melt channel.

The at least one distributor channel for the first melt can be connecteddownstream via a bore in the dividing sleeve to the annular outer meltchannel. The dividing sleeve can have further distributor channels,preferably branched distributor channels on the other surface in orderto distribute the first melt efficiently and uniformly to the annularouter melt channel.

The co-injection nozzle can also have a plurality of first and secondmelt supply channels which are each connected via distributor channelsto the respective annular melt channels. This allows an efficient anduniform distribution of the melts to annular melt channels having largediameters of more than 40 mm.

The co-injection nozzle, in particular in relation to the branching ofthe distributor channels, the additional distributor channels on thedividing sleeve and/or the plurality of melt supply channels for thefirst and second melt can be considered to be an independent inventionin itself. This is also independent of the configuration of the nozzlecore, in particular independent of whether the nozzle core only extendsas far as the nozzle mouth or protrudes beyond the nozzle mouth andthereby completely or partially forms a part of the cavity or whether itis cooled or not cooled. The advantage of such a co-injection nozzlelies in that it allows an annular injection with substantially greaterdiameters than hitherto possible. Combined with the previously describednozzle core, for example containers having a diameter of more than 40 mmcan also be injected annularly from the broad side or from theperipheral side, which had not been possible hitherto.

The invention further relates to a hot-runner nozzle for one or moremelts (i.e. a hot-runner nozzle for a single injection or for aco-injection) for an injection moulding tool, wherein the hot-runnernozzle has an annular nozzle mouth, a nozzle core and a hollow needledisplaceable along the nozzle core for opening and closing the annularnozzle mouth. The nozzle core protrudes beyond the annular nozzle mouthof the hot-runner nozzle and in the installed state of the hot-runnernozzle, the nozzle core forms a core of a cavity of the injectionmoulding tool. The nozzle core can be configured as describedpreviously.

The invention further relates to a method for producing aninjection-moulded part having an inner and an outer shape using aninjection moulding tool described previously. The method can comprisethe following steps: a) closing the injection moulding tool to form acooled cavity for the injection-moulded part to be injected byintroducing the nozzle core of the hot-runner nozzle into the cooleddie; b) injecting at least one melt into the cooled cavity through anannular nozzle mouth running around the nozzle core; and c) opening theinjection moulding tool and ejecting the injection-moulded part.

In the case of co-injection of several melts as a layered melt flowwith, for example, a barrier layer as inner layer, firstly only thefirst melt can be injected and only then the layered melt flow.

BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in detail hereinafter with reference toexemplary embodiments in connection with the drawing(s). In the figures:

FIG. 1 shows a sectional view of an injection moulding tool;

FIG. 2 shows a side view of a melt distributor insert;

FIG. 3 shows a side view of a melt distributor insert with dividingsleeve; and

FIG. 4 shows a detailed view of a hot-runner nozzle in the area of thenozzle mouth.

WAYS FOR IMPLEMENTING THE INVENTION

The injection moulding tool comprises a die plate 1 which forms the die1 a for the cavity 3 and a core plate 2 which receives a hot-runnernozzle 4. The hot-runner nozzle 4 has an annular nozzle mouth 5 and ahollow needle, wherein the nozzle mouth 5 can be opened and closed bythe hollow needle 6. To this end, the hollow needle 6 is guided movablyalong an axially non-movable nozzle core 7. The nozzle core 7 protrudesbeyond the annular nozzle mouth and forms the core 2 a of the cavity 3.

In the embodiment shown the nozzle core 7 comprises an inner coolingcore 8 which is actively cooled with a cooling medium, in particularwater, and an outer core 9. The downstream-directed end of the outercore 9 and the downstream-directed front face 10 of the cooling core 8form the core 2 a of the cavity 3, i.e. they correspond to the negativeof the inner shape of the injection-moulded part to be produced. Theouter core could also form the entire front face of the core 2 a. In theembodiment shown, upstream of the nozzle mouth, the nozzle core 7 has aninsulating jacket 11 which is made of ceramic or a less heat-conductingmetal alloy (e.g. a chromium steel) than the metal alloy for the heatedparts of the hot-runner nozzle 4. The insulating jacket 11 reduces theheat transfer between the hot parts of the hot-runner nozzle 4 and thecooled nozzle core 8 or outer core 9. This heat transfer is additionallyreduced by a circumferential recess 12 on the jacket surface of theouter core 9 and upstream of the nozzle mouth 5. The insulating jacket11 extends as far as the nozzle mouth 5. The hollow needle 6 is guidedalong the insulating jacket 11 of the nozzle core 7. The hot-runnernozzle can have more than one insulating jacket.

In the embodiment shown in FIG. 1, the insulating jacket 11 extends asfar as the cavity 3. FIG. 4 shows a detailed view of the hot-runnernozzle in the area of the nozzle mouth (circle A in FIG. 1). Unlike thehot-runner nozzle in FIG. 1, the outer core 9 of the hot-runner nozzlefrom FIG. 4 has a circumferential flange 13 in the area of the nozzlemouth 5. The circumferential flange 13 forms a part of the cavity 3 sothat the cavity 3 is completely formed by the cooled die plate 1, thecooled core plate 2 and the cooled nozzle core 7 of the hot-runnernozzle 4. The insulating jacket 11 in this case extends only as far asthe circumferential flange 13 and insulates the cooled nozzle core withrespect to the heated parts of the hot-runner nozzle 4. In theco-injection nozzle shown, as will be described in detail hereinafter,these are a nozzle body 30, a melt distributor insert 31, a dividingsleeve 32 and a retaining and sealing sleeve 33. Depending on theconfiguration of the cavity, the circumferential flange can also beconfigured as a shoulder on which the insulating jacket rests.

The hot-runner nozzle can be designed for one melt or for several meltsas a co-injection nozzle. In the embodiment of FIG. 1 which is shown,the hot-runner nozzle is configured as a co-injection nozzle for atriply layered melt flow having two outer layers of a first melt A andan inner layer, e.g. a so-called barrier layer, of a second melt B. Inthe front region upstream of the annular nozzle mouth, the co-injectionnozzle has an annular inner melt channel 20, an annular central meltchannel 21 and an annular outer melt channel 22. The annular inner 20and the annular outer melt channel 22 are fluidically connected to atleast one melt supply channel 23 a, 23 b for the first melt A. Theannular central melt channel 21 is fluidically connected to at least onemelt supply channel 25 for the second melt B (cannot be identified inFIG. 1 because it is arranged in front of and behind the plane ofintersection).

The co-injection nozzle 4 shown in FIG. 1 comprises a nozzle body 30, amelt distributor insert 31, a dividing sleeve 32, and a retaining andsealing sleeve 33 (or sealing ring). The nozzle body 30 is provided witha heating element 34. FIG. 2 shows a side view of the melt distributorinsert from FIG. 1. FIG. 3 shows a side view of the melt distributorinsert 21 and the dividing sleeve 22 from FIG. 1.

The co-injection nozzle 4 has a central bore which extends axiallythrough the melt distributor insert 31 and in which the hollow needle 6is movably received. The central bore has a larger diameter in a centralto lower region (i.e. downstream) than in the upper region (i.e.upstream) so that the annular inner melt channel 20 is formed along thehollow needle 6. The hollow needle 6 can also be tapered in this regionin order to enlarge the cross-section of the annular inner melt channel20. Also only the hollow needle can be configured to be tapered and thecentral bore can have the same diameter over the entire length. Anon-movable nozzle core is arranged inside the hollow needle 6. This canbe configured as the previously described cooled nozzle core 7, protrudebeyond the nozzle mouth 5 of the hot-runner nozzle 4 in the flowdirection of the melt and form a cooled core 2 a in the core plate 2 ofthe injection moulding tool which forms the inner form for the innershape of the injection-moulded part to be produced.

The annular central melt channel 21 is formed by an outer surface of thedistributor insert 31 and an inner surface of the dividing sleeve 32.The annular outer melt channel 22 is formed by an outer surface of thedividing sleeve 32 and an inner surface of the retaining and sealingsleeve 33.

In the embodiment shown the annular inner melt channel 20 is connectedupstream fluidically to two first melt supply channels 23 a, 23 b forthe first melt A. Downstream it is connected fludically to a nozzlemouth 5. The first two melt supply channels 23 a, 23 b for the melt Aeach lead from a first melt supply opening on the upper side of the meltdistributor insert 31 partially through the nozzle body to the annularinner melt channel 20. Furthermore, in each case at least one meltdistributor channel 24 a (in FIG. 1 only the upper end can beidentified) for the melt A is connected fluidically to the first twomelt supply channels 23 a, 23 b and conducts the respective melt A intothe common annular outer melt channel 22.

The melt A is therefore guided via the two melt supply channels and therespective melt distributor channels into the common annular inner meltchannel 20 and the common annular outer melt channel 22.

Furthermore, in the embodiment shown the co-injection nozzle 4 comprisestwo second melt supply channels for the second melt B (cannot beidentified in FIG. 1). In FIGS. 2 and 3 one of the two melt supplychannels 25 a is indicated by an arrow and its end can be identified onthe outer surface of the melt distributor insert 31. The two melt supplychannels for the second melt B lead like the first two melt supplychannels 24 a, 24 b for the melt A from respective melt supply openingson the upper side of the melt distributor insert 31 partially throughthe nozzle body 30 to respectively at least one melt distributor channelfor the second melt B. The melt distributor channels for the second meltB are fluidically connected downstream to the common annular centralmelt channel 21.

Both the melt distributor channels for the first melt A and also themelt distributor channels for the second melt B are formed on the outersurface of the distributor insert (e.g. by milling) and are delimited inthe direction radially outwards by the inner surface of the nozzle body30 or the dividing sleeve 32.

The melt distributor channels 24 a for the first melt A end above theannular central melt channel 21. Via a through-opening 27 in thedividing sleeve 32 they are each connected to melt distributor channels28 formed on the outer surface of the dividing sleeve 32, which arefinally fluidically connected to the annular outer melt channel 22.Alternatively the bores can also lead directly into the annular outermelt distributor channel 22.

In order in particular in the case of a large diameter of the annularnozzle opening 5 to distribute the melts A, B uniformly on the annularouter and central melt channel 21, 22, the respective melt distributorchannels on the outer surface of the distributor insert 31 can have abranching or bifurcations, as shown for example in FIGS. 2 and 3. Themelt distributor channels on the dividing sleeve 32 can also have abranching or bifurcation. After each branching or bifurcation thecross-section of the channels can be reduced in order to achieve anapproximately uniform flow rate over the entire flow section.

The annular melt flows from the annular inner, central and outer meltchannels 20, 21, 22 are combined shortly before the outlet through thenozzle mouth 5 to form a concentrically layered melt flow which finallypasses through the nozzle mouth 5 into the cavity 3.

REFERENCE LIST

-   1 Die plate-   1 a Die-   2 Core plate-   2 a Core-   3 Cavity-   4 Hot-runner nozzle-   5 Annular nozzle mouth-   6 Hollow needle-   7 Nozzle core-   8 Cooling core-   9 Outer core-   10 Front face-   11 Insulating jacket-   12 Circumferential recess-   13 Circumferential flange-   20 Annular inner melt channel-   21 Annular central melt channel-   22 Annular outer melt channel-   23 a, 23 b Melt supply channel for melt A-   24 a Melt distributor channel-   25 a Melt supply channel for melt B-   26 a Melt distributor channel for melt B-   27 Through opening-   28 Melt distributor channel on dividing sleeve for melt A-   30 Nozzle body-   31 Melt distributor insert-   32 Dividing sleeve-   33 Retaining and sealing sleeve/sealing ring-   34 Heating element

1. An injection moulding tool for producing an injection-moulded partwith an outer shape and an inner shape comprising a cavity and ahot-runner nozzle connected to the cavity having an annular nozzle mouthfor injecting at least one melt into the cavity; wherein the cavity isformed by a cooled die which forms an outer form for an outer shape ofthe injection-moulded part to be produced and by a core which forms aninner form for an inner shape of the injection-moulded part to beproduced; and wherein the hot-runner nozzle has a nozzle core and ahollow needle which is displaceable along the nozzle core for openingand closing the annular nozzle mouth, wherein the nozzle core protrudesbeyond the annular nozzle mouth of the hot-runner nozzle and thatwherein the nozzle core forms the core of the cavity of the injectionmoulding tool.
 2. The injection moulding tool according to claim 1,wherein the nozzle core comprises an inner cooling core and an outercore.
 3. The injection moulding tool according to claim 1, whereinupstream of the nozzle mouth of the hot-runner nozzle, the nozzle corecomprises an insulating jacket along which the hollow needle is guided.4. The injection moulding tool according to claim 3, wherein theinsulating jacket is made of ceramic, a low heat-conducting metal or alow heat-conducting metal alloy.
 5. The injection moulding toolaccording to claim 2, wherein the outer core has a circumferentialshoulder or a circumferential flange in the region of the nozzle mouth,which forms one side of the nozzle mouth.
 6. The injection moulding toolaccording to claim 2, wherein upstream of the nozzle mouth the outercore has a circumferential recess.
 7. The injection moulding toolaccording to claim 1, wherein the hot-runner nozzle is a co-injectionnozzle for injection of a concentrically layered melt flow into thecavity.
 8. The injection moulding tool according to claim 1, wherein acooled die plate forms the die.
 9. The injection moulding tool accordingto claim 1, wherein the core is cooled and is arranged in a cooled coreplate.
 10. The injection moulding tool according to claim 1, wherein thehot-runner nozzle is mounted in the cooled core plate by a sealing ring.11. A hot-runner nozzle for an injection moulding tool, wherein thehot-runner nozzle has an annular nozzle mouth, a nozzle core and ahollow needle displaceable along the nozzle core for opening and closingthe annular nozzle mouth, wherein the nozzle core protrudes beyond theannular nozzle mouth of the hot-runner nozzle and wherein the nozzlecore in the installed state of the hot-runner nozzle forms a core of acavity of the injection moulding tool.
 12. The hot-runner nozzleaccording to claim 11, wherein the nozzle core comprises an innercooling core and an outer core.
 13. The hot-runner nozzle according toclaim 11, wherein upstream of the nozzle mouth of the hot-runner nozzle,the nozzle core comprises at least one insulating jacket along which thehollow needle is guided.
 14. (canceled)
 15. A method for producing aninjection-moulded part using the injection moulding tool according toclaim 1, comprising the following steps: a) closing the injectionmoulding tool to form a cooled cavity for the injection-moulded part tobe injected by introducing the nozzle core of the hot-runner nozzle intothe cooled die; b) injecting at least one melt into the cooled cavitythrough an annular nozzle mouth running around the nozzle core; and c)opening the injection moulding tool and ejecting the injection-mouldedpart.